It is common practice to apply chemicals to a growing crop, for instance to help control pests, fungi or weeds.
Ground-based crop-spraying equipment commonly comprises a vehicle-carried body, e.g. a tractor-carried body, having an elongate framework or boom which extends laterally from the body and which supports nozzles which apply a spray mist of chemical/water mixture to the crop and its surroundings. Such a boom is often used to cover working width of between 12 and 30 meters to minimise the number of passes required to cover a given area of land.
The requirement for such an elongate boom causes the designer of crop-spraying equipment many problems in dealing with the stresses imposed on the boom and its supporting framework and on the carrying vehicle. There is also the problem of maintaining a distance between the boom and the ground (or growing crop) whilst the carrying vehicle is travelling over uneven ground.
Prior types of equipment have attempted to resolve the problems using various mechanisms.
Previous designs are known which use a single pivotal connection between a carrying frame supported on the carrying vehicle and the boom which allows the boom to swing in the manner of a pendulum independently of the carrying frame. With this type of design it is possible for conditions to occur which cause the boom to swing uncontrollably and it is common practice to add springs and shock-absorbers between the carrying frame and the boom to afford some degree of control. This has the effect of tending to make the boom attempt to follow the movements of the carrying frame on the one hand and attempt to follow the horizon on the other hand. The resultant compromise angle is not always desirable.
The addition of springs and shock-absorbers is beneficial in that the boom tends to follow the angle of the carrying frame (rather than following the horizon) when operating on a side-incline (or when the vehicle's wheels on one side are in a deeper rut than on the other side) but also causes an unwanted effect when conditions occur which require the boom to be set at an angle differing to that of the carrying frame. This can commonly occur, for example, when the suspension of the carrying vehicle or frame tends to cause the boom to favour the horizontal rather than following the angle of its wheels.
An alternative known method adds a levelling bar to the above pendulum mechanism to allow the neutral pendulum point (that is where the springs on both sides of the pendulum pivot apply an equal force) to be biased to one side or the other. This allows the machine operator (or an automatic mechanism) to reset the correct distance between boom and ground for the duration of the aforesaid conditions. This mechanism commonly takes the form of a rocker bar pivoted on the carrying frame, the springs being attached to this bar rather than to the carrying frame.
The present invention seeks to provide means to enable the boom more closely to follow the contours of the ground by at least partially isolating the boom from the movements of the carrying vehicle.
An object of the invention is to seek better to isolate the boom from movements of the carrying frame while retaining the beneficial effects of the boom tending to follow the angle of the carrying frame and also retaining the ability to bias the neutral pendulum point.